25Mar 2019 by Grant Fritchey 1 Comment

Can You Force A Parallel Plan in Query Store?

SQL Server 2016, SQL Server 2017
I love the questions I get when presenting: Can You Force a Parallel Plan in Query Store. I haven't a clue. The trick I think is going to be in setting up the test. Let's try it out. Reliably Getting a Parallel Plan Because this is for testing, rather than try to build some crazy query that may or may not go parallel, I've decided to cheat. I'll take advantage of a little functionality that ensures I see a parallel plan when I want to. Here's my code: DBCC TRACEON(8649); GO SELECT soh.OrderDate, soh.ShipDate, sod.OrderQty FROM Sales.SalesOrderHeader AS soh JOIN Sales.SalesOrderDetail AS sod ON sod.SalesOrderID = soh.SalesOrderID WHERE soh.SalesOrderID = 43705; GO DBCC TRACEOFF(8649); Traceflag 8649 will force all plans to go parallel by effectively making the Cost Threshold for…
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01Jun 2015 by Grant Fritchey 4 Comments

Parallelism and Columnstore Indexes

T-SQL
Columnstore indexes are fascinating and really cool. Unfortunately, they're adding an interesting new wrinkle to an old problem. What's the Cost Threshold for Parallelism set to on your server? If you just said "The whatsis of whositz?" then the value is 5. The cost threshold is the point at which the estimated cost of an execution plan goes from definitely serial to possibly parallel. This default was set for SQL Server 2000 and hasn't been changed since. I've long argued, loudly, that it's too low. I've suggested changing it to a much higher value. My advice has gone from 35 to 50 and several places in between. You could just look at the median or the mode of costs on your system and use the higher of those values as…
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05Aug 2013 by Grant Fritchey 19 Comments

Be Cautious Offering Guidance

Azure, SQL Server, T-SQL
Guidance is hard. Seriously, you'd think it would be easy. You'd think you say things like, don't shrink your database, most tables should have a clustered index, never go against a Sicilian when death is on the line, don't mix sharks and tornados, and that would be it. You'd be done. But it's not that easy. Even worse, it's SHOCKINGLY easy to get stuff wrong. An example. I was looking at information over at Microsoft Developers Network (MSDN) in the SQL Server Books Online. I was reading through information about wait types when I found this little beauty: Occurs when trying to synchronize the query processor exchange iterator. Know what that is? Yeah, OK, a few of you who memorize wait stats do (shut up Tom), but most of us…
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